1. Field of the Invention
The invention is related to an electrical connector assembly which comprised an electrical connector and a pick up cap, the pick up cap being mounted to the connector for providing a flat top surface to be engaged by a vacuum suction device, whereby the connector can be moved onto a circuit substrate such as a printed circuit board (PCB) on which the connector is to be mounted.
2. Description of the Prior Art
At present, on many production lines of the electrical indirty materialry, electronic components such as electrical connectors are mounted onto circuit substrates such as printed circuit boards (PCBs) by surface mount technology (SMT), as disclosed in U.S. Pat. Nos. 5,615,477 and 4,916,805.
A method of mounting an electrical connector onto a PCB by SMT generally comprises a sequence of the following steps A through F:    A—Application of an adhesive film on the PCB having a plurality of metal contact pads. The application of the adhesive film may be performed by screen printing, pin transfer, or from a dispenser onto predetermined areas of the PCB.    B—Activation of the adhesive film by irradiation with actinic light in the ultraviolet (UV) or visible wavelength ranges between 200 and 600 nm, to a degree and for a period of time such that a desired initial tackiness is produced.    C—Mounting the connector with its contacts on the activated adhesive film and the metal contact pads of the PCB.    D—Curing the adhesive film at a temperature between 60˜140° C.; for example, in a convection cabinet, using infrared radiant heaters or by means of the actinic radiation source used in step B if such source also produces infrared radiation.    E—Producing electrical engagement between the contacts of the connector and the corresponding metal contact pads of the PCB by soldering in a wave solder machine or in drag soldering equipment;    F—Cooling the assembly to room temperature.
In step C, the connector is accurately positioned on the PCB by a vacuum suction device. Generally, a typical connector has a multiplicity of holes in a flat top portion thereof. Thus the connector does not have a suitably smooth, integral top surface for engagement by a vacuum suction device. Typically, a pick up cap is attached on the top portion of the connector to provide the required plane top surface, as disclosed in U.S. Pat. No. 6,478,588.
Referring to FIG. 6, there is shown an assembled and isometric view of a conventional electrical connector 8 and a convention pick up cap 9 mounted onto the connector 8. The connector 8 comprises a frame 81, an insulative housing 84 received in the frame 81, a load plate 82 mounted on an end of the frame 81, and an operation member 83 mounted on an opposite end of the frame 81 and capable of engaging with the load plate 82. The housing 84 defines a number of cells (not shown) therethrough, the cells receiving a corresponding number of electrical contacts (not shown). The contacts are soldered onto a PCB (not shown) with electrically connecting with a plurality of metal contact pads formed on the PCB. The pick up cap 9 has a planar body 91 with an integrated smooth top surface and four latches 92 extending downwardly from the planar body 91. The latches 92 clasp edges of the load plate 82 of the connector 8 to mount the pick up cap 9 onto the connector 8. A vacuum suction device (not shown) can engage the top surface of the pick up cap 9 to move the whole assembly to a desired location on the PCB. Then the connector 8 can be heated and soldered onto the PCB.
However, the pick up cap 9, the frame 81 and the load plate 82 cover the housing 84. When curing the adhesive film at a high temperature in a convection cabinet using infrared radiant heaters, heated air can only flow through a gap between the pick up cap 9 and the connector 8, the cells of the housing 84 to a bottom portion of the housing 84. Generally, the time needed for curing the adhesive film is short. Thus, the adhesive film is liable to cure non-uniformly. When this happens, electrical engagement between some of the contacts and the corresponding metal contact pads of the PCB may be flawed. The connector 8 may not reliably electrically connect with the PCB. Additionally, when cooling the entire assembly to room temperature, heated air can only be dissipated out through the gap between the pick up cap 9 and the connector 8. This increases the time needed for cooling the assembly, which reduces the efficiency of mounting of the connector 8 onto the PCB.
Referring to FIG. 7, for settling the above-mentioned problems, another pick up cap 6 is provided. The pick up cap 6 has four generally rectangular vents 60 extending through the planar body 61 in a vertical direction thereof. When curing the adhesive film at high temperature in a convection cabinet using infrared radiant heaters, heated air can flow through the vents 60 and get to a bottom of the connector 8 quickly. Therefore, the connector 8 can be reliably electrically soldered onto the PCB in a short time, and the efficiency of mounting of the connector 8 onto the PCB is improved. However, a new problem appears because of the vents 60 in the pick up cap 6. Dirty material is liable to adhere to the contacts of the connector 8 through the vents 60, which effects performance of the contacts.
In view of the above, a new pick up cap that overcomes the above-mentioned disadvantages is desired.